In the modern industrial age, there are many facilities that make, store, or dispense materials that may be harmful to the environment if discharged. Examples of such facilities include without limitation fuel stations for dispensing fuel to automobiles, trucks, airplanes, locomotives, etc. (a neighborhood gasoline station is one example of such a fuel station); factories for making chemicals, plastics, steel, or any product in which the process of manufacture involves the use of a material that may be harmful to the environment; storage facilities for fuel, chemicals, or any potentially harmful or dangerous material. Improved methods and systems for detecting discharges from such facilities are needed.